The present invention relates to a mono-color editing method for color picture image recording apparatuses, such as color copying machines, color facsimiles, and color printers, and more particularly to a mono-color editing method for a color picture image recording apparatus having the function of color editing process.
Digital color copying machines are provided with a picture image reading means for reading an original sheet by scanning it, a picture image editing means for processing and editing the picture image data thus read, a picture image output means for recording the picture image data processed and edited, and a control means, which controls the picture image reading means, the picture image editing means, and the picture image output means, and are capable of executing various editing processes on the picture image data with the picture image editing means. Further, digital color copying machines have come to employ highly advanced digital color picture image processing techniques in the recent years, so that such machines have realized a large number of color picture image editing functions.
A mono-color converting process is available as one of picture image editing processes for converting an achromatic picture image into a chromatic picture image while maintaining its tonal gradation intact. However, the conventional color picture image recording apparatus performs a color picture image editing process at the stage at which the picture image data are in the form of a picture image in the three primary colors, namely, blue (B), green (G), and red (R), or at the stage at which the picture image has been converted into picture image data in the four toner colors, namely, yellow (Y), magenta (M), cyan (C), and black (K). Therefore, it has hitherto been necessary to perform very complicated processing operations for the execution of mono- color conversion, namely, the processing operations necessary for converting the hue while maintaining the tonal gradation intact and it has also been necessary to take a long period of time for such processing operations.
Hence, for the present invention, it is an object to offer a mono-color editing method which enables a color picture image recording apparatus in a simple construction to execute the mono-color converting process with ease, thereby overcoming the above-mentioned disadvantages of the conventional method.
The mono-color converting process is an editing process which changes only the color in a state in which the tonal gradation of an achromatic picture image is kept intact. Thus, it is considered that the process can be executed with ease, for example, by converting picture image data in the three primary colors, B, G, and R into picture data representing the luminance, hue, and chroma, which are expressed by V, H, and C, respectively, and then converting only the hue into that of a designated color. However, as an achromatic picture image has such a low chroma that a conversion of only the chroma would still result in nothing other than a picture image quite similar to an achromatic picture image.
Therefore, the present invention proposes a method which consists in generating picture image data in the four toner colors by multiplying the luminance signal V with a coefficient for realizing a specified mono-color in response to instructions for the execution of the mono-color converting process.
A color picture image recording apparatus for practicing the mono-color editing method according to the present invention is provided with a matrix means 1 and a multiplying means 2, as illustrated in FIG. 1A. It is to be noted that those editing operations other than the mono-color editing operation, such as color conversion and coloration (painting), are executed at a stage preceding the matrix means 1. A luminance signal L* and two color difference signals a* and b* for a uniform color space are fed into the matrix means 1. Then, the matrix means 1 puts out only the luminance signal L* out of the input picture image data in case the control signal has given instructions for performing a mono-color editing operation, but put outs the toner color signals, which respectively express the toner colors, Y, M, C, and K, out of the above- mentioned signals L*, a*, and b*, in case the control signal instructs otherwise.
The multiplying means 2 multiplies the picture image data put out of the matrix means 1 with a prescribed coefficient. The multiplying means 2 multiplies the picture image data with a coefficient for permitting the toner color signals, which are thus put out of the matrix means 1, to pass through in case the control signal does not give any instruction for the execution of any mono-color editing operation, but generates the four toner color signals for Y, M, C, and K by multiplying the input luminance signal L* with four coefficients respectively corresponding to the color as instructed by the control signal in case the control signal has given instructions for a color editing operation.
Various forms are conceivable for the forms of the coefficients with which the multiplying means 2 multiplies the input picture image data, but the form of such coefficients to be used by the method according to the present invention will be in the form of data expressing the coverage of the toner colors, Y, M, C, and K, namely, the number of dots to be developed per unit area.
Moreover, it is to be arbitrarily determined how many of mono-colors should be made available. For example, in case a converting process is set up for using fifteen mono-colors, it will be sufficient to distinguish sixteen different states including the through state, and the control signal will then be in four bits.
Further, the available methods in which such a coefficient is to be set in the multiplying means 2 include the following. One is a method consisting in setting such a coefficient by a CPU which performs overall control over the picture image processing operations including the mono-color converting process. In this case, the CPU mentioned above recognizes the mono-color which the user has sets and gives a coefficient for realizing the particular mono-color in the form of a control signal at each time to the multiplying means 2. Another method is a method, as shown in FIG. 1B, consisting in providing the multiplying means 2 with a table which contain the coefficients k.sub.Yi, k.sub.Mi, k.sub.Ci, and k.sub.Ki (wherein i=0, 1, 2, . . ., . . ., n) written thereto in respect of the individual monocolors registered as such and issuing a control signal indicating the mono-color for which a coefficient is to be used. In this case, the multiplying means 2 sets the coefficient for the mono-color thus indicated by the control signal, reads it out of the above-mentioned table.
Next, the operations for the output from the multiplying means 2 are as described below. In case an image output means arranged at a stage in the downstream side of the multiplying means 2 develops four toner colors in a single developing process, the image output means will be constructed in such a manner that it puts out picture image data on the four toner colors, Y, M, C, and K, at the same time, but, in case an image output means develops toner in one color by one developing process, thus finishing the picture images in full color in four cycles of its developing process, the multiplying means 2 will be constructed in such a manner as to put out the picture image data in a toner color appropriate for each developing process performed by the picture image output means.
Next, a description will be made of the control signal. The control signal is generated for every area for which the mono-color editing process is set up. For example, as shown in FIG. 1C, it is assumed here that a rectangular area 4 and a free-shape area 5 are set up on the original sheet 3, a red mono-color being specified for the area 4 and a green mono-color being specified for the area 5. Then, in respect of the area 4, a control signal indicating the red mono-color will be notified to the multiplying means 2 in synchronization with the picture image data read from the original sheet 3. That is to say, a coefficient indicating the red mono-color is put into the multiplying means 2 at the same time as the picture image data L* for the area 4 are put into the multiplying means 2. Thus, the coefficient for the red mono-color will be set in the multiplying means 2, by which the achromatic picture image in the area 4 will be converted into a red color picture image having the same tonal gradation. In the same manner, a control signal indicating a green color will be notified for the area 5, and also a control signal indicating "through" passage will be notified in any part of the original sheet other than the areas 4 and 5.
The control signals may be generated on the basis of a picture image recording job mode which the user has set. In other words, the user will set the menu to the effect that a mono-color editing process should be performed and also sets the color of the mono-color, thereby indicating what color the mono-color should be, in case an achromatic image in a desired area is to be converted into a chromatic image, a control signal can be generated on the basis of the setting of the picture image recording job mode which the user has thus set.
Moreover, as shown in FIG. 1D, the control signals may also be generated by once producing picture image data having luminance V, hue H, and chroma C from picture image data in the three primary colors, B, G, and R, then detecting with an window comparator 6 whether or not the V, the H, and the C are in their respective predetermined ranges, generating an achromatic color signal, which indicates that the particular pixel is achromatic, in case all of the V, the H, and the C are in their respective predetermined ranges at the same time, and then generating a control signal on the basis of the achromatic color signal.